'Non-conventional' gases are less carbon-intensive ('greener') alternatives to natural gas that are increasingly being added to natural gas supply networks. Determination of the composition of these gases is essential to ensure that the mixed gas streams transported in pipelines is 'interchangeable', i.e. it is able to be used in existing pipelines and with existing appliances.

NPL is developing analytical techniques and traceable standards to underpin measurements of the composition of the following families of non-conventional gases:

• Biogas
• Coal bed methane and coal mine methane
• Hydrogen-enriched natural gas

Biogas

Gases of biological original (often termed 'biogases', i.e. gases produced by anaerobic fermentation or digestion of organic matter) provide two analytical challenges:

1. Measurement of composition in order to ensure interchangability
   
   
2. Measurement of toxic impurities to ensure the health of the public

The table below [1] gives indicative compositions of biogases, and highlights some of the key impurities present. Analyses of biogases are carried out using GC methods such as GC-MS, GC-FID, GC-TCD and GC-SCD.

Species	Amount fraction / concentration
	Biogas		Biomass gasification
	Anerobic digester	Landfill	Oxygen fired	Air fired
Methane	50 - 80 %	30 - 60 %	0 - 18 %	1 - 10 %
Other hydrocarbons	-	-	0 – 5.8 %	0 - 2 %
Hydrogen	0 - 2 %	0 - 2 %	4 – 46 %	10 – 25 %
Carbon monoxide	-	-	13 – 70 %	9 – 25 %
Carbon dioxide	15 - 50 %	15 – 40 %	2– 35 %	7 – 16 %
Nitrogen	0 - 5 %	0 – 50 %	0 – 7 %	~ 50 %
Oxygen	0 – 1 %	0 – 10 %	-	-
Hydrogen sulphide	0.1 – 10 g.m-3	0 – 1 g.m-3	-	-
Ammonia	0 – 100 mg.m-3	0 – 5 mg.m-3	-	-
Total chlorine	0 – 100 mg.m-3	0 – 800 mg.m-3	-	-
Total fluorine	0 – 100 mg.m-3	0 – 800 mg.m-3	-	-
Siloxanes	0 – 50 mg.m-3	0 – 50 mg.m-3	-	-
Tar	-	-	0 - 5 g.m-3	0.01 - 100 mg.m-3

Note: All amount fractions are expressed as % mol/mol

Coal bed methane and coal mine methane

Coal-bed methane (CBM) is emitted from un-worked coal seams; coal mine methane (CMM) is emitted from exposed coal in worked coal seams. The compositions of CBM and CMM are similar to some natural gases, with oxygen also being present in CMM due to exposure of the coal seem to air. The table below [1] gives indicative compositions of CBM and CMM.

NPL supplies a range of high-accuracy gas standards for the analysis of CBM and CMM.

Species	Amount fraction / concentration
	CBM	CMM
Methane	65 %	90 %
Other hydrocarbons	1.5 %	2.2 %
Carbon dioxide	16 %	3.3 %
Nitrogen	18 %	4.5 %
Oxygen	0.5 %	-
Hydrogen sulphide	0 - 5 mg.m-3	0 - 5 mg.m-3

Note: All amount fractions are expressed as % mol/mol

Hydrogen-enriched natural gas

The edition of hydrogen to natural gas has the capability of reducing the carbon intensity of the gas if the hydrogen is generated using renewable energy sources. It has been found [2] that up to 20% hydrogen can be added to natural gas streams without compromising safety, or affecting the efficiency of boiler systems.

NPL supplies a range of high-accuracy natural gas standards for the calibration of natural gas analysers. Hydrogen can be added as an additional component in these mixtures if requested.

References

[1] Injection of gases from non-conventional sources into gas networks, MARCOGAZ document WG-Biogas-06-18, 2006.

[2] Using the existing natural gas system for hydrogen, report from the EC NATURALHY project, 2009.

Contact

For further information about NPL's capability in the area of non-conventional gases, please contact:

Customer Service tel: +44 20 8943 8637
E-mail: gases_enquiries@npl.co.uk